U.S. Pat. No. 3,676,555, issued to G. Schrader et al, discloses that compounds having the general formula (I) ##EQU1## wherein R is alkyl are excellent insecticides. These compounds are prepared from S-sodium-O-alkylphosphoroamidothioate by reaction with a methylating agent such as methyl iodide. The sodium salt, in turn, is obtained by the reaction of sodium hydroxide with an O,O-dialkylphosphoroamidothioate as illustrated in the following equation (1): ##EQU2## wherein R is alkyl.
Unfortunately the insecticides of formula (I) have relatively high mammalian toxicity and are therefore of limited use. U.S. Pat. No. 3,716,600, issued Feb. 13, 1973, to P. S. Magee, discloses that N-acylated derivatives, e.g., N-acetyl, of the compounds of formula (I) are of essentially equal insecticidal activity but are significantly less toxic to mammals. However, it has been found by experimentation that preparation of the new and safer insecticides of U.S. Pat. No. 3,716,600 from the sodium salt of the corresponding N-acylated phosphoroamidothioate was not possible because the sodium salt would not form upon the reaction of an O,O-dialkyl-N-acylphosphoroamidothioate with sodium hydroxide. Under mild conditions only starting material was recovered; and under more severe conditions, degradation occurred without the formation of the desired sodium salt.